Redis 源码走读（二）对象系统

Redis设计了多种数据结构，并以此为基础构建了多种对象，每种对象（除了新出的 stream 以外）都有超过一种的实现。

redisObject 这个结构体反应了 Redis 对象的内存布局

typedef struct redisObject {
    unsigned type:4;//对象类型
    unsigned encoding:4;//底层数据结构
    unsigned lru:LRU_BITS; /* LRU time (relative to global lru_clock) or
                            * LFU data (least significant 8 bits frequency
                            * and most significant 16 bits access time). */
    int refcount;
    void *ptr;//指向数据结构的指针
} robj;

可以看出，robj 用4个 bit 存储对象类型，4个 bit 存储对象的底层数据结构

其中对象类型有下面几种：

#define OBJ_STRING 0    /* String object. *///字符串类型
#define OBJ_LIST 1      /* List object. *///列表类型
#define OBJ_SET 2       /* Set object. *///集合对象
#define OBJ_ZSET 3      /* Sorted set object. *///有序集合对象
#define OBJ_HASH 4      /* Hash object. *///哈希对象
#define OBJ_MODULE 5    /* Module object. *///模块对象
#define OBJ_STREAM 6    /* Stream object. *///流对象，redis 5中新增

数据结构有下面几种：

#define OBJ_ENCODING_RAW 0     /* Raw representation *///基本 sds
#define OBJ_ENCODING_INT 1     /* Encoded as integer *///整数表示的字符串
#define OBJ_ENCODING_HT 2      /* Encoded as hash table *///字典
#define OBJ_ENCODING_ZIPMAP 3  /* Encoded as zipmap */ //废弃
#define OBJ_ENCODING_LINKEDLIST 4 /* No longer used: old list encoding. *//废弃
#define OBJ_ENCODING_ZIPLIST 5 /* Encoded as ziplist *///压缩列表
#define OBJ_ENCODING_INTSET 6  /* Encoded as intset *///整数集合
#define OBJ_ENCODING_SKIPLIST 7  /* Encoded as skiplist *///跳跃表
#define OBJ_ENCODING_EMBSTR 8  /* Embedded sds string encoding *///embstr
#define OBJ_ENCODING_QUICKLIST 9 /* Encoded as linked list of ziplists */
#define OBJ_ENCODING_STREAM 10 /* Encoded as a radix tree of listpacks */

其实观察 objectComputeSize 这个方法就看出对象与数据结构的关联关系

OBJ_STRING = OBJ_ENCODING_RAW + OBJ_ENCODING_INT + OBJ_ENCODING_EMBSTR

OBJ_LIST = OBJ_ENCODING_QUICKLIST + OBJ_ENCODING_ZIPLIST

OBJ_SET = OBJ_ENCODING_INTSET + OBJ_ENCODING_HT

OBJ_ZSET = OBJ_ENCODING_SKIPLIST + OBJ_ENCODING_ZIPLIST

OBJ_HASH = OBJ_ENCODING_HT + OBJ_ENCODING_ZIPLIST

OBJ_STREAM = OBJ_ENCODING_STREAM

Redis 源码走读（二）对象系统

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